1. Field of the Invention
The invention relates to nanoparticulate wax dispersions, a process for preparing them and a method for hydrophobing materials based on lignocelluloses and/or celluloses by means of contacting them with the wax dispersions.
2. Description of the Prior Art
It is frequently desired to reduce the water absorption and swelling tendency of absorbent materials such as wood-based materials or paper/cardboard products, or statutory provisions or customer requirements make it necessary to remain under the limits for water absorption and swelling tendency of such materials or processing products thereof. According to applicable European standards (DIN EN 622 and DIN EN 312), wood-based materials for example have to comply with certain requirements regarding the swelling in thickness during underwater storage and with regard to water absorption.
In order to comply with the required limits, many absorbent materials are provided with hydrophobing agents during the production process. The hydrophobing agent itself should not necessitate unnecessary water introduction and should not interfere with further processing of the material, especially if the hydrophobed feed materials are present in form of chippings, strands or fibers and the processing products are made from the strands, chippings or fibers by joining them together, for example by means of thermal setting, compressing or bonding with suitable binding agents.
The application of waxes onto or into such materials or feed materials thereof containing or consisting of lignocelluloses and/or celluloses as hydrophobing agents, also in form of aqueous dispersions, is known in principle. Optimization of the hydrophobing effect of wax dispersions, when used for example in wood-based materials, has until now primarily been effected by modification of the composition of the wax phase (compare EP 1 448 345-B1).
For hydrophobing wood-based materials consisting of lignocelluloses with paraffin, a number of studies are known. In this connection, it should be referred to the article by Roffael, E., Schriever, E., May, H.-A., Adhäsion 11 (1982), pp. 10-19, “Hydrophobierung von Spanplatten mit Paraffin”, Teil 1 and to the publication by May, H.-A. and Roffael, E. “Hydrophobierung von Spanplatten mit Paraffin”, Teil 4 (Adhäsion 28, (1, 2), 17-21). However, further improvements are desirable.